This application is based on application No. H10-212376 filed in Japan on Jul. 28, 1998, the entire content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a digital camera, and more particularly to a digital camera capable of flash shooting.
2. Description of the Prior Art
Conventionally, digital cameras are known that are provided with an image sensor having a two-dimensional array of CCDs (charge-coupled devices). A digital camera of this type senses the light coming from a subject and takes in, as an image signal, an electric signal whose level varies in accordance with the amount of the light sensed. In shooting, in accordance with the brightness of the subject, the exposure time (the shutter speed) and the aperture value of the CCD are set in such a way that, the lower the brightness of the subject, the wider the aperture and the longer the exposure time. In this way, shooting is performed under appropriate exposure conditions.
When the subject is so dark that, even if the aperture is made fully open and the exposure time is set at the maximum within the range that does not cause a hand shake (hereafter the exposure time thus set is referred to as the maximum hand-shake-free period), the subject image taken suffers from underexposure, flash shooting is performed by emitting flash light during photoelectric conversion to illuminate the subject. Flash shooting is performed with the exposure time fixed at a predetermined value, for example 1/60 seconds. The brightness of the subject is controlled by adjusting the amount of the flash light emitted. Some cameras adopt automatic light amount adjustment in which the flash light reflected from the subject is detected to stop flash light emission when the amount of light detected reaches a predetermined value.
The image signal obtained from the image sensor is converted into a digital signal, and is thereafter subjected to color adjustment, i.e. white balance adjustment, in order to faithfully reproduce the white areas of the image. In normal shooting without flash light emission, white balance adjustment is performed for every image in accordance with the color characteristics (wavelength distribution) of ambient light. On the other hand, in flash shooting, white balance adjustment is performed uniformly in accordance with the color characteristics of the flash light.
Quite naturally, there is an upper limit to the amount of flash light a flash can emit. Moreover, the farther the subject lies away from the camera, the less flash light the subject receives. Thus, when the subject lies considerably far away from the digital camera, even if the maximum amount of flash light is emitted, it is impossible to illuminate the subject to appropriate brightness, with the result that the subject image taken suffers from underexposure. In such a case, in most conventional digital cameras, the subject can not be shot with appropriate exposure; that is; even if the subject is illuminated with flash light, degradation of the image quality is inevitable.
An object of the present invention is to provide a digital camera that can shoot an image with appropriate exposure irrespective of the distance to the subject even in flash shooting and that can achieve proper white balance adjustment in images shot by flash shooting at all times.
To achieve the above objects, according to one aspect of the present invention, a digital camera is provided with a photoelectric conversion device, a flash, and a time setter. The photoelectric conversion device senses light from a subject to generate image data of the subject. The flash emits light to illuminate the subject. The time setter sets, when shooting is performed using the light emitted by the flash, a photoelectric conversion time for which the photoelectric conversion device performs photoelectric conversion in accordance with the distance to the subject. When the subject is close to the camera, it can be illuminated to appropriate brightness with the flash light, even if the photoelectric conversion time is set to be short as in the conventional cameras. In the camera, when the subject is too far away from the camera to be illuminated to the predetermined brightness with the flash light, it is possible to set the photoelectric conversion time to be longer so that a large amount of ambient light is utilized for illuminating the subject. Thus, irrespective of the distance to the subject, it is always possible to obtain images in which the brightness of the subject is appropriate.
According to another aspect of the present invention, a digital camera is provided with a photoelectric conversion device, a flash, a first time setter, a second time setter, a first balance adjuster, and a second balance adjuster. The photoelectric conversion device senses light from a subject to generate image data of the subject. The flash emits light to illuminate the subject. The first time setter sets, when shooting is performed using the light emitted by the flash, a photoelectric conversion time for which the photoelectric conversion device performs photoelectric conversion to be equal to a predetermined length of time when the distance to the subject is equal to or shorter than a predetermined distance that corresponds to the guide number of the flash. The second time setter sets, when shooting is performed using the light emitted by the flash, the photoelectric conversion time for which the photoelectric conversion device performs photoelectric conversion to be longer than the predetermined length of time when the distance to the subject is longer than the predetermined distance. The first balance adjuster performs white balance adjustment on the image data generated by the photoelectric conversion device based on the color characteristics of the light emitted by the flash when the distance to the subject is equal to or shorter than the predetermined distance. The second balance adjuster performs white balance adjustment on the image data generated by the photoelectric conversion device based on the color characteristics of ambient light when the distance to the subject is longer than the predetermined distance. When flash shooting is performed with the predetermined photoelectric conversion time, the flash light becomes dominant in illuminating the subject. In contrast, when flash shooting is performed with the photoelectric conversion time longer than the predetermined photoelectric conversion time, the ambient light becomes dominant in illuminating the subject. Since white balance adjustment is performed based on the color characteristics of the dominant light, it is always possible to obtain images of good color quality.
According to still another aspect of the present invention, a digital camera shoots an image by means of a photoelectric conversion device and is capable of performing flash shooting by emitting flash light to illuminate a subject, during photoelectric conversion. In flash shooting, in this digital camera, when the subject lies within the distance range in which the flash light can illuminate the subject with predetermined brightness, the photoelectric conversion time for which the photoelectric conversion device performs photoelectric conversion is set to be equal to a predetermined length of time, and, when the subject lies outside the predetermined distance range, the photoelectric conversion time for which the photoelectric conversion device performs photoelectric conversion is set to be longer than the predetermined length of time.